In pulp drying of a web, integration of cooling capacity with the drying concept has become common quite quickly. One of the reasons for this rapid acceptance of cooling/drying integration is a process-technical reason, for example, the reliability of operation of a slitter. Recently, a more important reason has been the introduction of a chlorine-free production process (TCF) in which the brightness of the pulp is initially somewhat inferior to that of pulp bleached with chlorine. Baling or reeling when the web is excessively hot results in manila coloring of the paper produced from the web, as a result of which the brightness of the paper, which is an important criterion of quality, is lowered.
Cooling capacity is provided in existing machines by adding separate cooling units in connection with the pulp dryer. In new machines, the cooler is more and more frequently constructed as an integrated part of the dryer proper.
As the art progresses, stricter requirements are imposed on the prevention of noise generated by paper machines and particularly pulp dryers. In particular, in the paper-making industry, in various machine halls, the prevention of noise has been dealt with in a number of different locations. In view of the prevention of noise, particularly demanding objects are the mills of pulp industry, in particular the cooling layer in a pulp dryer.
An air cooler for pulp is based on a technique in which air from the machine hall or cooled air is blown through air nozzles against the web face. The air is introduced into the cooler by means of blowers which may be either attached to the side of the cooler/dryer or separate devices placed at a distance from the cooler/dryer unit. Most commonly, in both cases, the blown air is discharged from nozzle gaps freely into the machine hall. In such a case, the noise of the blowers, nozzles, and the other process noise have access to be spread freely into the machine hall. Of course, in the other respects, a pulp dryer is a heat-insulated and thus, at the same time, a partly sound-insulated closed unit, whose noise level does not become very high.
The noise from the blowers and from the air flow in the cooling layer of a pulp dryer has free access into the machine hall. In some cases (and with stricter regulations, more and more often) this results in a noise level that is not within permissible limits.
The sound attenuation/insulation in the cooling layer in a pulp dryer is important, for a pulp dryer machine is, even otherwise, a noisy process in which it is important to avoid additional noise and to eliminate existing noise.